A high resolution SPECT detector based on thin continuous LYSO

Abstract

Single-photon emission computed tomography (SPECT) detectors with improved spatial resolution can be used to build multi-pinhole SPECT systems that have a higher sensitivity or a higher spatial resolution. In order to improve the spatial resolution we investigate the performance of a 2 mm thick continuous Lutetium Yttrium Orthosilicate (LYSO) scintillator and compare it to the performance of a 5 mm thick continuous NaI(Tl) scintillator. The advantages of LYSO are its high stopping power and its non-hygroscopicity. Drawbacks are the lower light output and the intrinsic radioactivity. The hypothesis of this study is that such a thin LYSO scintillator will have a small light spread and, as a consequence, will also have an improved spatial resolution when coupled to a Hamamatsu H8500 position sensitive photomultiplier tube. To optimize the spatial resolution and the useful detector area we used a mean nearest neighbor event-positioning method. Beam source measurements ((99m)Tc, 140 keV) were done to investigate the energy resolution and the spatial resolution of both detectors. The effect of the intrinsic radioactivity of the LYSO scintillator in the energy window was quantified. The mean energy resolution is 9.3% for the NaI(Tl) scintillator and 21.3% for the LYSO scintillator. The LYSO spectrum shows an X-ray escape peak which decreases the detection efficiency with 9.1%. The spatial resolution of the LYSO detector (0.93 mm full width at half maximum (FWHM)) is superior to the spatial resolution of the NaI(Tl) detector (1.37 mm FWHM). The intrinsic radioactivity in the energy window (42% window centered at 140 keV) is low (125.6 cps, 0.024 cps mm(-3)). LYSO is a promising scintillator for small-animal SPECT imaging, where spatial resolution is more important than energy resolution.

Performance characterization of a compact SPECT detector based on dSiPMs and monolithic LYSO

“…This value is also confirmed by calculating the average FWHM resolution using the point grid. If we compare the intrinsic resolution obtained here, 0.486 mm, to the intrinsic resolution for the PSPMT-based detector reported by Deprez et al[3], 0.784 mm, it is clear that an almost 40 % better resolution can be obtained with the DPC-based detector. This difference can be explained by the presence of smaller pixels in the DPC detector.…”

“…Since LYSO has a higher density (7.10 g/cm 3 ) than NaI(Tl) (3.67 g/cm 3 ), using this type of scintillator permits the use of thinner crystals, while still achieving the same stopping power. At the same time, we believe that, because there is less light spread in thinner crystals, they will lead to a better spatial resolution [3]. Detectors with a high intrinsic resolution allow the use of pinhole minification instead of magnification, making it possible to build systems with a higher sensitivity than current state-of-the-art systems while still obtaining a comparable system resolution [4], [5].…”

“…Even though some literature discourages the use of LYSO for SPECT because of its intrinsic radioactivity [6], in our setup the effects caused by the background activity of a thin crystal will be limited since the activity is proportional to the crystal volume and therefore these effects do not outweigh the benefits of higher detection efficiency. In a previous study using position sensitive photomultipliers, it was already shown that, although using LYSO results in a worse energy resolution than using NaI(Tl), it has a more uniform and better spatial resolution [3], [7]. The aim of this work is to investigate the use of the DPCs from Philips Digital Photon Counting combined with thin, monolithic LYSO scintillators as a compact SPECT detector.…”

Development of clinical simultaneous SPECT/MRI

“…22 Further preclinical systems have been developed through academic/industrial collaborations and the SPECT–MRI interaction has been evaluated. 8,40–42 A preclinical SPECT system has been designed using Lutetium Yttrium Orthosilicate and digital SiPM; 43 the high-density detector enables use of a thin detector for SPECT with the potential to reduce depth of interaction effects that are common with pinhole collimation. However, the light output is somewhat compromised for low-energy gamma emitters.…”

Design and development of a dedicated portable gamma camera system for intra-operative imaging

“…However, by calculating the energy spectrum of each crystal cell and by normalizing them using the peak shift method, an improved total normalized energy spectrum was obtained [24,25]. So this configuration of small gamma cameras often has a FWHM energy resolution that is poorer than single crystal scintillation cameras [26][27][28][29]. However, we believe that the scintillator array we used in this work has a relatively poor energy resolution.…”